The present invention relates to fiber optic cross connects, and more particularly to the redirection and scanning lengths used to perform the switching operation by fiber optic cross connects.
The use of optical cross connect (OXC) switching systems are well known in the art for directing a light beam from one optical port in an optical transmission system to another optical port. In a typical OXC, a plurality of input optical fibers, or ports, carry light beams into the OXC. The OXC then directs, or switches, the light beams to their respective plurality of output ports. Many conventional OXCs perform the switching utilizing micromirrors, which are micro-machined onto a substrate. The micromirrors are used to reflect a light beam from an input port to a particular output port. In this specification, the words xe2x80x9cinputxe2x80x9d and xe2x80x9coutputxe2x80x9d are used to indicate a direction of travel for a light beam into and out of, respectively, a switch. In reality, the input and output ports can be used simultaneously for input and output, as is the case in bi-directional data transfer.
High port count switches utilizing micromirrors are of high demand in the industry. Such switches require a tight packing density of the micromirrors onto the substrate. Some conventional switches use a digital switching matrix for N input and N output ports with an Nxc3x97N array of micromirrors. This requires a total of N2 number of micromirrors. However, this architecture becomes impractical for switch port counts greater than a few hundred.
Some conventional switches use an analog switching matrix for N input and N output ports. This requires 2*N micromirrors. In this configuration, two separate substrates, or one very large substrate, are necessary to accommodate port counts greater than a few hundred. However, the use of more than one substrate is cumbersome as they need to be aligned to each other within the package of the switch. This adds complexity to the assembly of the package and increases package size. Also, with a hundred or more micromirrors on a single substrate, or one half of a two-substrate OXC, device yield is compromised due to the large number of possible failure points. Additionally, the optical components of the OXC are typically hermetically sealed. Such hermetic sealing of the optical components requires additional complex steps in the manufacturing process, such as metallization of the fibers or optical component attached to the fibers.
For many conventional switches, each micromirror also utilizes different amounts of the Rayleigh Length for redirecting light beams. The Rayleigh Length is a maximum distance that a beam of light can be kept collimated. The Rayleigh Length depends on the wavelength and minimum diameter xe2x80x9cwaistxe2x80x9d of the beam. The Rayleigh Length is well known in the art and will not be described in detail here. This xe2x80x9credirection lengthxe2x80x9d, as used in this specification, is typically the length from a collimator to an input mirror and from an output mirror to another collimator. The remaining portion of the Rayleigh Length, i.e., the length from the input mirror to the output mirorr, is available for scanning. Because the redirection length varies from micromirror to micromirror, the scanning length also varies. This requires the switch to be designed so that the longest redirection length is assumed for all micromirrors in the switch in order to minimize optical loss and crosstalk. However, in assuming the longest redirection length for all micromirrors, the density of micromirrors is compromised.
Accordingly, there exists a need for an improved OXC package which minimizes optical loss and crosstalk while also reducing the size of the package. The present invention addresses such a need.
The present invention provides a method and an optical cross connect (OXC) package which minimizes optical loss and crosstalk while also reducing the size of the package. The method includes directing a light beam from a first collimator of a plurality of collimators to a first micromirror of a plurality of micromirrors; folding the light beam from the first micromirror onto a second micromirror of the plurality of micromirrors; and directing the light beam from the second micromirror to a second collimator of the plurality of collimators, wherein a uniform redirection length is provided between each of the plurality of collimators and each of the plurality of micromirrors. In the preferred embodiment, the OXC package comprises a first cap with reflecting surfaces and a second cap. With the first cap, only a short distance is used in redirecting the light. This allows for the major portion of the light to be available for scanning. With the second cap, the light beam is folded during the switching operation, resulting in a smaller switch package.